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Molon
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Posted: 10/21/2010 11:43:14 AM
(Reposted in order to update. The original thread went to archive.)


5.56mm NATO versus .223 Remington Chamber Differences


A SAAMI spec .223 Remington chamber will have a shorter leade with a sharper angle to the leade and a shorter amount of effective freebore than a 5.56mm NATO chamber. The freebore itself will also be narrower in the .223 Remington chamber.


raw pics courtesy of Ned Christiansen


With all other things being equal, the 5.56mm NATO chamber with its longer and shallower angled leade and longer amount of effective freebore will produce less chamber pressure than a .223 Remington chamber, when firing .223 Remington SAAMI Spec ammunition. Because of this, 5.56mm NATO amunition can be loaded to a pressure that would be considered excessive in a .223 Remington chamber, yet acceptable in a 5.56mm NATO chamber. (Pressures are measured using different methods between the two systems.)


The leade of a SAAMI 223 Remington chamber.






from Rifle magazine



The official SAAMI 223 Remington drawing.








From Jeff Hoffman, co-owner of Black Hills Ammunition

“The 5.56 IS a higher pressure/velocity cartridge, but it is made to a military standard, with different test methods, (and therefore is not easily directly comparable to .223 pressures) . . . the general spec for US 5.56 ammo is 58,700 psi max, measured at case mouth. . . Please note this is a different method than SAAMI transducer or copper crusher, as used on commercial ammunition. 5.56 ammunition spec results in ammunition loaded to a higher pressure level than commercial .223, but the test methods specified are different . . .The spec calls for a different pressure test method than SAAMI spec ammo, and is not directly comparable . . . “


Here's a very interesting quote posted by Ned Christiansen on M4carbine.net:


". . . In short, you can safely fire all 5.56 AND 223 ammunition in a gun properly chambered for 5.56. You MUST NOT fire 5.56 ammunition in a 223 rifle. As case in point, I fired XM193 5.56 ammunition in a 223 test barrel with average pressures (conformal transducer) of 72,550 psi, and peak pressure registered at 76,250 psi. . ."

Since the SAAMI MAP for the .223 Remington is 55,000 PSI, that puts XM193 fired from a minimum spec .223 Remington chamber at 17,550 PSI over the maximum.


(The following is just a generalization to give a graphical demonstration of concept. DO NOT hold me to the exact numbers as they are not correct and they ignore the difference due to the different methods used to measure chamber pressure.)

Consider the left graph pictured below; M193 fired in a 5.56mm chamber. The pressure is within the MAP limit. Now, take the exact same round, (same powder, same charge of powder) and fire it from a .223 Remington chamber; pictured in the right graph below.

Because the .223 Remington chamber has a shorter and sharper angled leade compared to the 5.56mm chamber as well as a shorter effective free-bore, the bullet engages the rifling sooner in the .223 chamber than it would have in a 5.56mm chamber. This causes the pressure to rise faster, peak sooner and reach a higher (and per SAAMI, unsafe) level than it would have if the round had been fired from a 5.56mm chamber.





Many people seem to incorrectly believe that 5.56mm brass cases have significantly reduced case capacity compared to .223 Remington cases. The table of case capacities shown below demonstrates that this notion is false.












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Zhukov
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Posted: 10/21/2010 12:15:24 PM

Originally Posted By Molon:
(Reposted in order to update. The original thread went to archive.)

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Pain
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Posted: 10/21/2010 2:31:14 PM
To add to Molons post, many manufactures, i.e. Rock River Arms, Larue Tactical and others run a Wylde chamber.

What's a Wylde chamber?
The .223 Wylde chamber was designed as a match chambering for semi-automatic rifles. It will accomodate both .223 Rem and 5.56mm NATO ammunition. It is relieved in the case body to aid in extraction and features a shorter throat for improved accuracy.
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reelserious
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Posted: 11/21/2010 8:29:14 PM
Originally Posted By Pain:
To add to Molons post, many manufactures, i.e. Rock River Arms, Larue Tactical and others run a Wylde chamber.

What's a Wylde chamber?
The .223 Wylde chamber was designed as a match chambering for semi-automatic rifles. It will accomodate both .223 Rem and 5.56mm NATO ammunition. It is relieved in the case body to aid in extraction and features a shorter throat for improved accuracy.




What specifically is "relieved" in the case body. How much relieved over regular dimensions?
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Posted: 3/14/2012 8:27:39 AM
You have probably heard this a million or two times but I am new to the AR style rifles and I have two one for my grandson and one for me, an AP-4 and a Mini Sass, I will not mention the manufacturer as maybe that is a no no here, I am also new to AR15.com. I was interested in the tested pressures of these rifles and also just what type of chamber were cut in them, they are marked on the barrel 5.56 however I understand that there are different styles of chambers cut into these rifles and could be any of them. I then called the manufacture and ask a tech those two questions, the answer I got back just left me with a question mark, his responce was they are both 5.56 and the pressure you can get from the SAAMI web site??? What??? he would not go any further with me and I was nicely dismissed as he had no further comment, is this normal? what the hey!! Maybe these are stupid questions I dont know and what does the SAAMI web site have to do with NATO chambers? I have been trying to read as much as possible about the AR, must not have learned enough. Any insight I can get on this would help because I would like to reload for these rifles.
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Posted: 3/14/2012 9:15:09 AM
Thanks for posting this. It clears up the question of .223/5.56 for me in a very straightforward way.
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Posted: 3/14/2012 9:15:50 AM
[Last Edit: 3/14/2012 9:16:14 AM by 1saxman]
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Posted: 3/14/2012 9:51:08 AM
With this info in mind and noticing how HOT barrels get with just 50 rounds, IMO, running 5.56x45 in a .223 designed barrel is going to result in some fatigue further down the line.
Unlike my pistols, it appears AR-15 style rifles need closer attention when either purchasing or reloading ammunition. Thanks for this invaluable information.

On a somewhat related note, I've noticed a few head-space checkers on the internet (MidwayUSA or Brownells) and wondering if it is worth getting the GO and NO-GO checkers? My first carbine just arrived yesterday (no, I didn't assemble mine) but I will be doing my own assembled AR-15 later in the year so as part of the "tool kit" so to speak, was curious about these checkers.
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Posted: 3/14/2012 12:20:10 PM
Suggest sticky and FAQ. Great info as usual!
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Posted: 10/13/2012 11:50:05 AM
This is a great explanation and the photos really show the difference. Nice work. But the one question that I can't seem to find an answer for that I really trust is about my early (1970's) Colt SP1. It's marked 223/5.56. I called Colt to ask about the NATO ammo and got an "it's all OK" kind of answer. Didn't the NATO chambering start AFTER my SP1 was built? Or more specifically, how were the Vietnam era barrels, such as my old SP1, chambered? Should I stick to XM193 ammo or just shoot anything it?

Thanks, jim.
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Posted: 12/21/2012 9:42:54 PM
So I get it's "bad" to fire a .223 round in a 5.56 chamber, but ok going the other way.

I guess I'm a bit confused because of the markings on my rifle.....My Bushmaster AR-15 is marked .223/5.56 on the lower and the barrel is marked MP 5.56 with 1/9 twist. My question is....what markings should I really be going by to be on the safe when buying ammo? It's not modified in anyway, Bought it new in factory sealed box from a friend/local dealer. My friend has been selling me .223 and 5.56 ammo for it. I have shot both thru it with no issues so far.
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Posted: 12/21/2012 9:56:06 PM
[Last Edit: 12/21/2012 9:57:58 PM by America-first]
Originally Posted By 1badedge540:
So I get it's "bad" to fire a .223 round in a 5.56 chamber, but ok going the other way. You have it backwards; you can fire .223 in a 5.56 chamber albeit with a slight decrease in accuracy.

I guess I'm a bit confused because of the markings on my rifle.....My Bushmaster AR-15 is marked .223/5.56 on the lower and the barrel is marked MP 5.56 with 1/9 twist. My question is....what markings should I really be going by to be on the safe when buying ammo? It's not modified in anyway, Bought it new in factory sealed box from a friend/local dealer. My friend has been selling me .223 and 5.56 ammo for it. I have shot both thru it with no issues so far.


Your Bushmaster is chambered for 5.56 so you can safely shoot both that and .223.
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Posted: 12/21/2012 10:37:17 PM
Thanks for clarifying that, much appericiated!!....I either read the OP wrong at that time or things got switched around in my brain while I was typing that...lol
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Posted: 12/21/2012 10:46:50 PM
Originally Posted By 1badedge540:
Thanks for clarifying that, much appericiated!!....I either read the OP wrong at that time or things got switched around in my brain while I was typing that...lol


The markings on the lower are immaterial; many lowers are marked "MULTI" because there is little beside magazine well dimensions that has anything to do with what cartridge a rifle is chambered for. On the other hand, the barrel's markings say without question, not just what cartridge the chamber is cut for, but (usually) the rifling twist and sometimes even the kinds of testing (MP, HP, etc) the barrel has undergone.
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Posted: 1/28/2013 5:42:04 PM
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Posted: 1/28/2013 6:25:45 PM
Nice to see you post in the tech forum again. Your regular informative posts are sorely missed.
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